(1) Field of the Invention
The present invention relates to a method of treating a fine particle dust in a manufacturing process of semiconductor elements and an apparatus therefor, and particularly to the method of treating a fine particle dust in a manufacturing process of semiconductor elements and the apparatus therefor which may catch the fine particle dust having a diameter of more than 0.01 .mu.m for a long time and to dispose of it.
(2) Prior Art
Recently, computers and electric control devices utilizing the computers have been progressed remarkably, and it seems that development of these industries expands widely and infinitely. Now, a technique in manufacturing semiconductors, which takes an important position as electronic parts used for a computer, and also the gross of its production are growing remarkably and rapidly.
Germaneium (Ge) and silicon (Si) are normally used as raw materials for the semiconductor elements, and as a special semiconductor element, gallium-arsenic (GaAs) and gallium-phosphorus (GaP) and the like are utilized.
The processes for manufacturing semiconductor elements comprises, for example, a column forming process for forming a column of the semiconductor, a wafer forming process for slicing the column of the semiconductor, an element forming process forming a number of elements by repeating the processes of masking the wafer, forming a thin film thereon, doping and etching the same, and a cutting process for cutting the treated wafer into each of the elements.
In the manufacturing processes, it is known that very fine particle dust of such as 0.01.about.50 .mu.m is generated. It is also known that such fine particle dust is sometimes harmful and disposal is prohibited in view of prevention of enviromental pollution, and the gas itself including such a fine particle dust is harmful. Further, the fine particle dust sometimes absorbs or adsorps a harmful substance.
The harmful substances generated or used in the semiconductor manufacturing are such as silicon, arsenic, phosphorus, boron, metallic hydrogen, fluorine, halogen, halide, nitrogen oxides and the like, which will be referred to below.
As the silicon harmful gas, it may typically form monosilane (SiH.sub.4), dichlorosilane (SiHCl.sub.2), silicon trichloride (SiHCl.sub.3), silicon tetrachloride (SiHCl.sub.4), silicon tetrafluoride (SiF.sub.4), disilane (Si.sub.2 H.sub.6), or TEOS(Si(OC.sub.2 H5).
As the arsenic harmful gas, it may form arsine (AsH.sub.3), arsenic fluoride (III) (AsF.sub.3), arsenic fluoride (V) (AsF.sub.5), arsenic chloride (III) (AsCl.sub.5), or arsenic chloride (V) (AsCl.sub.5).
As the phosphorus harmful gas, it may form phosphine (PH.sub.3), phosphorus fluoride (III) (PF.sub.3), phosphorus fluoride (V) (PF.sub.5), phosphorus chloride (III) (PCl.sub.3), phosphorus chloride (V) (PCl.sub.5 s), or phosphorus oxychloride (POCl.sub.3).
As the boron harmful gas, it may form diborane (B.sub.2 H.sub.6), boron trifluoride (BF.sub.3), boron trichloride (BCl.sub.3), or boron tribromide (BBr.sub.3).
As the metallic hydrogen harmful gas, it may form hydrogen selenide (H.sub.2 Se), monogermane (GeH.sub.4), hydrogen telluride (H.sub.2 Te), stibine (SbH.sub.3), or hydrogen tin (SnH.sub.4).
As the fluorine harmful gas, it may, for example, form methane tetrafluoride (CF.sub.4), methane trifluoride (CHF.sub.3),, methane difluoride (CH.sub.2 F.sub.2), propane sixfluoride (C.sub.3 H.sub.2 F.sub.6), propane octafluoride (C.sub.3 F.sub.8).
As the harmful gas of halogen and halide, it may form fluorine (F.sub.2), hydrogen fluoride (HF), chlorine (Cl.sub.2), hydrogen chloride (HCl), carbon tetrachloride (CCl.sub.4), hydrogen bromide (HB), nitrogen trifluoride (NF.sub.3), sulfur tetrafluoride (SF.sub.4), sulfur sixfluoride (SF.sub.6), tungsten sixfluoride (VI)(WF.sub.6), molybdenum sixfluoride (VI) (MoF.sub.6), germanium tetrachloride (GeCl.sub.4), tin tetrachloride (SnCl.sub.4), antimony pentachloride (V)(SbCl.sub.5), tungsten sixchloride (VI)(WCI.sub.6) or molybdenum sixchloride (VI)(MoCl.sub.6).
As the harmful gas of nitrogen oxides, it may form nitrogen monoxide (NO), nitrogen dioxide (NO.sub.2), or dinitrogen oxide (N.sub.2 O), and as the other harmful gas, it may also form hydrogen sulfide (H.sub.2 S), ammonia (NH.sub.3), and trimethylamine ((CH.sub.3).sub.3 N).
Further, it is known that fine particle dust may be produced in such a gas including ethane (C.sub.2 H.sub.5), propane (C.sub.3 H.sub.8), which have inflammability, and nitrogen (N.sub.2), oxygen (O.sub.2), argon (Ar), nitrogen dioxide (NO.sub.2) and the like.
Nowadays, the mind of preventing a public nuisance is thoroghly permeated. In such a state, it cannot accept to directly discharge the exhaust gas including the above harmful components or fine particle dust into the air, and first of all it is required to remove the particle dust from the exhaust gas and give it suitable treatment so as to change the harmful gas to be a safe and clean gas.
Conventionally, to remove particle dust from an exhaust gas or the like, the priorart has been using a cyclone, a scrubber, a venturi scrubber, a bag filter, an electric collector, a looper and a settler. Therefore, it has been proposed to utilize these devices in order to remove the particle dust from the exhaust gas produced in a manufacturing process of semiconductor elements. However, a function for catching the particle dust is limited. In the case of the cyclone, the diameter of the particle dust caught is more than 3.0 .mu.m, and the scrubber is 1.0 .mu.m. I*n the case of the venturi scrubber, bag filter, and electric collector, the diameter is more than 0.1 .mu.m. also, the looper is 10 .mu.m and the setter is 50 .mu.m. It is a fact that these conventional devices cannot catch the fine particle dust having a diameter of 0.01.about.50 .mu.m.
Then, the inventor has reached an idea to use a filter having a mesh of 0.01 .mu.m, but the idea has the following problem.
Namely, it is impossible, at present, to form a filter having a mesh of 0.01 .mu.m since the present technique in manufacturing such a filter has just reached a level of producing a filter having at most a mesh of 1 .mu.m.
If it is possible to form a filter having a mesh of about 0.01 .mu.m, such a very small mesh of filter increases a pressure requirement. Therefore, to generate a flow for carrying the particle dust from a source of producing the fine particle dust to the filter, a very big discharging device of high capacity such as a very big blower or fan must be used. As the result, it is found that provision of such a very small mesh of filter is not practical since it necessitates a wide area of installation of the device and that its installation cost becomes high.
Further, since the fine particle dust is caught by the filter and its pressure becomes great for a short time, it becomes necessary to change the filter soon.
Then, prior to the present invention the inventor has researched and invented a method of treating a fine particle dust in a manufacturing process of semiconductor elements and an apparatus therefor, in which an air, introduced from a source of generating the fine particle dust, is filtered by a laminated filter which is formed by laminating more than three filters arranged such that a smaller mesh filter is located down stream of the flow of the air. It is recognized in the test result of this method and apparatus that the particle dust having a diameter of 0.01 .mu.m can be caught certainly as it is expected (See Japanese patent laid-open publication No. 6-296815).
However, it was recognized through repetition of the text that choking of the laminated filter was accelerated more than the inventor had expected and that it necessitated changing of the filter frequently.
Then, the inventor further researched and found that the acceleration of choking the filter was bought by the following fact. Namely, an air including the fine particle dust produced in the process of manufacturing semiconductor elements, included liquids such as an oil leaked from a vacuum pump or an oil rotary or an aqua or oilish liquid for polishing or cutting. The liquids were floating in the state of very small fine mist, and stuck to the inside wall of a duct while the air blown in the duct and separated therefrom due to the flow of the air and then transferred to the laminated filter while they are mixing with the fine particle dust, so that the liquids were adhered to the laminated filter and choked the same.